Nonaqueous electrolyte batteries using, as a negative electrode, a lithium metal, lithium alloy, a lithium compound or a carbon material are anticipated to be used as high energy density batteries or high output density batteries, and much research and development has taken place therefor. Lithium ion batteries have been put into practical use, such as in a positive electrode containing LiCoO2 or LiMn2O4 as an active material and a negative electrode containing a carbon material capable of absorbing and releasing lithium.
Recently, use of a titanium oxide instead of a carbon material in the negative electrode has been studied, in terms of long cycle life, and high safety and reliability. When titanium oxide is used as a negative electrode active material, lithium is absorbed and released at a potential of 0.4 V (vs. Li/Li+) or more in a negative electrode, and thus aluminum or aluminum alloy can be used for a current collector, thus advantageously resulting in realization of more weight saving and lower cost.
On the other hand, a polarity inversion phenomenon in which a negative electrode potential becomes higher than a positive electrode potential occurs upon over-discharge. In addition, when the over-discharge is continued, oxidative decomposition of an electrolytic solution occurs at the negative electrode and reductive decomposition of the electrolytic solution occurs at the positive electrode, thus resulting in occurrence of a problem in which a battery temperature is elevated due to continuous heat generation.